The proposed studies of the function of the SV40 t-antigen will depend, in large part, on two observations made in studies of SV40 deletion mutants that lack t-antigen. First, the t-antigen appears to convert permissive CV-1 cells to theophylline resistance following infection and allows the cells to overcome a block to cell cycle progression imposed by this drug. Second, the SV40 t-antigen and similar antigens of other papovaviruses interact specifically with two cellular proteins of unknown function. A better understanding of t-antigen function may be obtained by more thorough definition of the conversion of CV-1 cells to theophylline resistance, particularly as studied in cell lines that express t-antigen, and by defining the functions of the cellular proteins in uninfected cells. Independent purifications of the t-antigen and the two cellular proteins will also be completed, and will provide a source of the proteins to be used in the exploration of specific functional questions. The functions to be investigated in early stages of this research will include those which might explain the pleiotropic nature of t-antigen effects on the host cell, and include potential binding of cyclic nucleotides and other nucleotides by the proteins and specific alterations in cyclic AMP related enzymes of the cell.